1. Field of the Invention
This invention relates to a high-speed, high-force electromagnetic actuator and more particularly, to an electromagnetic actuator for opening and closing a valve of an internal combustion engine wherein a velocity of the armature is controlled upon landing against a stator core of the actuator.
2. Description of Related Art
A conventional electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes an electromagnet which, when energized, produces an electromagnetic force on an armature. The armature is biased by a return spring and the armature is coupled with a cylinder valve of the engine. The armature is held by the electromagnet in one operating position against a stator core of the actuator and, by deenergizing the electromagnet, the armature may move towards and into another operating position by the return spring.
In an attempt to control the landing velocity of the armature, in certain electromagnetic actuator systems, power to a coil of the actuator is applied to move the armature across a gap and when the armature is approaching the stator core, a magnetic force from the coil is removed to slow down the armature and hope for a quiet or "soft" (near zero velocity) landing. Just before landing, the stator coil is reenergized to draw the armature towards and land at the stator core.
In the this type of arrangement, landing of the armature at a stator core is quite harsh and may have a velocity of approximately one meter per second. However, a required velocity value of the armature at landing calculated to provide acceptably quiet actuator operation is less than 0.04 meters per second at 600 engine rpm and less than 0.4 meters per second 6,000 engine rpm.
Accordingly, there is a need to provide control of an armature of an electromagnetic actuator to ensure that the armature completes its travel during its stroke but at the same time produces a quiet or "soft" (near zero velocity) landing of the armature against a stator core so as to prevent excessive impact wear on the armature and stator core and to reduce the amount of noise produced by such impact.